This section is intended to introduce the reader to various aspects of art, which may be related to the present embodiments that are described below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light.
Wireless communication networks are present in many communication systems today. Many of the communication devices used in the systems include one or more antennas for interfacing to the network. These communication devices often include, but are not limited to, set-top boxes, gateways, cellular or wireless telephones, televisions, home computers, media content players, and the like. Further, many of these communication devices may include multiple interfaces for different types of networks. As a result, one or more antennas may be present on or in a communication device.
As communication devices continue to get smaller in size, the space allocated in a communication device for communication circuitry, including the antenna(s), may also be reduced. The size or space required for an antenna may vary depending on a number of factors, including the communication network and the choice of antenna type used. One particular operational scenario involves using an inverted f antenna in a 2.4 gigahertz (GHz) home wireless network. FIGS. 1A-1C illustrate an exemplary inverted f antenna design incorporated onto a printed circuit board located inside a communication device. The inverted f antenna uses the top and bottom conductive copper layers of a multilayer printed circuit board. The conductive copper layers are joined together with interlayer vias to form the elements of the antenna.
FIG. 1A includes a conductive element 105. Element 105 operates with similar characteristics to a monopole antenna over a ground plane. One end of element 115 connects to element 105 at a point that is a predetermined distance from one end of element 105. The other end of element 115 connects to element 120. Element 120 is the interface point to an electrical circuit, such as the connection point to a communication circuit. The length of element 105 is selected to be approximately one quarter wavelength of the operating frequency of the antenna. The distance from the end of element 105 to the connection point with element 115 is chosen such that the radiation resistance is as close as possible to the operating impedance or resistance for the communication circuit connected to element 120. The end of element 105 closest to element 115 is connected to one end of another conductive element 110. The other end of element 110 is further connected to a conductive copper ground plane 125. The addition of element 110 is important to the structure of an inverted f antenna. Since the antenna length is usually selected to be less than a full wavelength of the operating frequency for the antenna, the electrical interface for the antenna may electrically operate equivalent to a resistive element in series with a low value capacitive element. Element 110 electrically operates similar to adding an inductor in parallel with the remaining equivalent elements in the antenna. As a result, element 110 reduces the effect of the equivalent series capacitance for the antenna. Although the addition of series capacitance may be used to reduce the size of the antenna, the position and amount of additional series capacitance may also lead to undesirable effects, including a degradation in antenna impedance or resistance and a degradation in antenna radiation pattern.
FIG. 1B includes a mirror image of the elements 105, 110, and 125, labeled 106, 111, and 126 respectively. FIG. 1b does not include elements 115 and 120. The mirrored elements 105, 106, 110, and 111 in FIG. 1A and FIG. 1A are connected together using vias 130a-n. The mirrored ground planes 125 and 126 in FIG. 1A and FIG. 1B are connected together using vias 135a-n. The vias 130a-n and 135a-n are spaced at a small fraction of the wavelength for the operating or resonant frequency of the antenna. As a result, the mirrored sets of elements effectively act and operate as a single set of elements. The other ends of elements 105 and 106 are left open or not connected. These ends of elements 105 and 106 are also maintained at a distance from the conductive ground planes 125 and 126 such that any undesired or stray capacitance is kept to a minimum in order to have a negligible effect on the tuned or resonant frequency of the antenna.
FIG. 1C shows a three-dimensional view of the elements described for FIG. 1A and FIG. 1B.
A printed circuit board antenna, such as the inverted f antenna described in FIGS. 1A-1C, additionally relies on characteristics associated with elements and materials around the antenna in order to determine the relationship between antenna physical parameters and antenna electrical operation parameters. Physical parameters, including the size, thickness, and length of the elements, along with conductivities and dielectric constants for materials used with the antenna, determine the electrical operating frequency for the antenna. The antenna in FIGS. 1A-1C relies on the dielectric constant value associated with air (e.g., a dielectric constant value equal to one) as one of the physical parameters to determine the electrical parameters and, as a result, determine the physical parameters for, or size of, the constructed antenna. However, an antenna with small physical parameters is desirable given the ever increasing constraints on space in a device, as described earlier. Therefore, there is a need to develop a printed circuit board antenna that is smaller in physical size than conventional printed circuit board antennas while maintaining the same or similar electrical operating parameters.